Engraving machine



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ENGRAVING MACHINE Filed Sept. 27, 1955 2 Sheets-Sheet 1 IL I A $44 v TONE A JOURCE Ph'drflCELL 22 P AMPLIFIER powER CONTROL AMPLIFIER I To: Z0 CONTROL Pawn? AMPLIFIER S. M. Paint/W INVE'NT OR BY Wm ATTORNEY April 7, 1959 s. M. FAIRCHILD ENGRAVING MACHINE 2 Sheets-Sheet 2 Filed Sept. 2'7, 1955 ig- .F .a-B "E Z aMFmim, WWW m INVENTOR BY WWW W ATTORNEY United States Patent ENGRAVING MACHINE Sherman M. Fairchild. New York, N.Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application September 27, 1955, Serial No. 536,969 Claims. (Cl. 178-66) This invention relates to automatic engraving machines of the type used for the production of relief printing plates or the like automatically from photographic or other originals, and more particularly to a means and method for improving the quality of the reproductions obtained from such automatically produced engraved plates.

An automatic engraving machine of the type to which this invention is particularly applicable is shown and described in U.S. Reissue Patent 23,914 to Boyajean, owned by the assignee of this invention. As disclosed in that patent such apparatus may comprise a first (engraving) cylinder for supporting a plate to be engraved, a second (scanning) cylinder for supporting an original or image sheet, and means for rotating both cylinders synchronously. The apparatus further includes a first reciprocable carriage including an electro-optical pick-up system for scanning the image sheet on the scanning cylinder, and a second reciprocable carriage including a plate deforming tool in the form of a heated stylus for engraving a plate on the engraving cylinder, both such carriages being reciprocated simultaneously. The Boyajean apparatus also is provided with an electrical screen generator for producing the correct stylus action to achieve a regular dot pattern or half-tone image.

The electro-optical system includes a light source energized by signals from the screen generator (although the screen tone may be introduced in other ways), the light being reflected from the original copy to a photocell whose amplified output drives the plate deforming tool in order to form on the plate an engraved half-tone image corresponding to that on the original copy. The carriages of both the pick-up system and the tool carriage are driven at identical rates by a tensioned inelastic belt as fully illustrated in the Boyajean patent. Also, the tool carriage includes a tool actuating assembly carrying the engraving tool and means for biasing the stylus vibrated by the tool assembly into engagement with the plate cylinder. The device is also provided with an adjustable pressure shoe for engaging a sheet or plate on the plate cylinder for determining the neutral position of the engraving tool. The output of the screen generator is adjustable to vary the minimum deformation of the plate corresponding to the black level of an image sheet, and provision is made for adjusting the output of the pick-up independently to adjust the maximum deformation of the plate corresponding to the white level of an image sheet.

For half-tone reproduction of photographs or other originals, which often consist of large unbroken surfaces and include many tones between a black and a relatively pure white, it is necessary to make a plate which will carry the image as a half-tone reproduction consisting of a large number of small raised peaks or dots. These dots provide the necessary printing surface, and variation in the dot size results in the reproduction of the various tones included in the original copy. To obtain these raised dots it is necessary to lower the remaining area of the plate by removing the plate material between the dots. In the photo-engraving process this is accomplished by chemically etching a metal plate. In the type of process to which this invention pertains, however, the result is accomplished by burning the excess material from the plate, which is composed of a suitable plastic material. In both processes, raised dots of varying size (but identical height) are used for making impressions on paper. Light toned or highlight areas of the photograph to be reproduced are broken down into tiny dots with considerable space between them which will show up as white when the plate is inked and used to print on paper. Dark or shadow areas are represented by large dots with little space between them. Since a photograph is composed of many tones and shades of gray, ranging often from a full white to a solid black, a plate made from such a picture will contain a dot pattern ranging from spaced tiny pin-point dots through a broad, almost complete, solid printing surface.

It is well known that the smaller the area being printed, that is, the smaller the area of the dot on the engraved plate, the greater the local printing pressure per square inch will be, and hence at areas of small dot size, the resulting printed product will be darker than expected on the basis of dot size and spacing alone. Since the highlight dots, those corresponding to the highlight or white portions of the photograph or copy being reproduced, are extremely small, they will tend to print darker than desired. To overcome this tendency, printers employ various techniques known as makeready; one common procedure involves the use of a very thin tissue which is cut out and placed upon (behind) the shadow portions of the engraved plate, thereby to increase the pressure per unit area of those portions so that the pressure per unit area exerted by the dots in the white or light areas will be in effect equalized to that in shadow areas. When carefully done, this provides improved re production and greater total tonal range.

Although such a means for building up the printing pressure at the dark areas of an engraved plate Works satisfactorily with plates made of metal, as for example, copper, the system is less effective on engraving plates made of plastic due to the difference in resiliency of the plate materials. In either case, considerable skill and hand labor are involved. Accordingly it is a principal object of this invention to provide a method and a system for automatically reducing the height of highlight dots only on an engraved plate.

It is another object of this invention to provide a photoengraving method and device which will produce engraved plates in which the highlight dots are selectively reduced in printing effectiveness from that normally achieved.

A further object of this invention is to provide a photoengraving method and device for selectively reducing the heights of the highlight dots of an engraving plate during the engraving process.

It is a further object of this invention to provide a photoelectric engraving machine in which the highlight dots of the plate being engraved are automatically and selectively reduced in height immediately after being formed to their normal height.

Still another object of this invention is to provide a photoelectric engraving machine in which the highlight dots are modified immediately after being formed, the modification being automatically accomplished by means of a material removing tool controlled by the light areas of the copy being reproduced on the engraving plate, and special circuit arrangements for this purpose.

More specifically stated, the invention provides a modification or improvement applicable especially to automatic plate engraving machines and processes, by which an auxiliary plate-deforming tool, herein called the makeready tool, is'caused to operate on the highlight areadots only, to lower their heights selectively. This tool may be controlled by the usual output signals operating the engraving tool, but means are provided to make the makeready tool effective only when and where needed. Thus, since the makeready tool will in all cases operate some time after the engraving tool proper, the usual output signal of the scanning operation will be subjected to such delay as is necessary to bring the makeready tool into operation at a point on the plate corresponding to the highlight area signals. The discrimination as to the existence of a highlight area needing makeready treatment is accomplished by a circuit which responds only when the scan signal magnitude exceeds a certain level arbitrarily established as corresponding to one boundary of the region constituting highlight conditions. This is so for a machine in which large scan signals correspond to white original copy areas and produce maximum plate penetration by the engraving tool. For a reversed machine (e.g., one operating from a negative original) the makeready tool would be operative when the scan signal falls below a certain value, as will be understood by those skilled in the art.

The above and other objects and advantages of this invention will be better understood when read in conjunction with the following specification and drawings in which:

Fig. 1 is a block diagram of the invention.

Fig; 2 is a perspective view of one embodiment of the invention.

Figs. 3A, 3B and 3C are views of other types of makeready tools that may be used with the modification illustrated in Fig. 2.

Fig. 4 is a fragmentary section view of a portion of a plate undergoing highlight modification.

Referring now to Fig. 1 of the drawings there is illustrated in block diagram form a system embodying this invention for producing on a plate a screened relief pattern suitable for image reproduction by printing processes, and on which plate the highlight printing dots will be' selectively reduced in height. By the term image sheet as used herein is meant any sheet carrying an optical representation of the image to be reproduced, such as a drawing, printed copy, photograph positive or negative print, a photographic transparency or the like. By screened relief pattern is meant a pattern in which regularly spaced portions of the surface are removed, the area of the removed portions in any elemental portions of the print varying with the shade values of the corresponding elemental portion of the image to be reproduced, as for example a half tone photo-engraved plate. The term printing as used herein refers to any pigment transfer process by which a plate carrying a screened relief pattern may be utilized to produce multiple reproductions, as for example the conventional letterpress printing process.

By makeready is meant a means or method for selectively reducing the effective height of the highlight dots'in light areas only of an engraved plate having a screened relief pattern thereon.

The system of Fig. 1 provides a light source to illuminate an image sheet 12 from which a screened relief pattern or engraving plate is to be made. Part of the light illuminating the image sheet 12 is reflected therefrom and strokes a photocell 14, the output of which is amplified by an amplifier 16 of any suitable conventional' type, an example of which can be found in the aforementioned Boyajean reissue patent. The amplifier may be designed to provide a linear gain characteristic. The output of the photocell amplifier is fed to two tone control units designated by the reference numerals 1 8 and 20 respectively. The tone control unit 18 may bedesigned to have an output v. input characteristic as illusvtrated in the block, that is, one in which the gain is high'at the low input portion of the response curye, the

gain decreasing over the middle range, and increasing again at the high input portion of the response curve. The output of the tone control amplifier 18 is fed to a conventional power amplifier 22. The output of the power amplifier 22 provides the power to energize a stylus motor 24 which drives an engraving stylus 26. The engraving stylus 26 may be heated by an electrical heating coil 28 which is independently mounted and powered, for use on plastic plates, or it may be a cold engraving or embossing tool. The signal path or system described up to this point is generally similar to the sys-' tem disclosed in the aforementioned Boyajean patent.

According to the invention, means are provided for selectivelyreducing the height of the highlight area printing dots. As stated above, a portion of the output of the photocell amplifier 16 is fed to a tone control circuit 20, the response characteristic of which is unlike that of the tone control 13 in that the tone control 20 is designed to have no output whatever until a relatively high level signal is impressed, after which the gain characteristic rises rapidly as illustrated in the block 20 of Fig. 1. The output of the tone control 20'is fed in a suitable delay system here shown as including a magnetic recording head 3% which causes a record to be made on the recording medium 32 which may be in the form of an endless magnetic tape, ring or drum. Displaced along the circumference of the ring 32 a distance equal to the displacement of a makeready tool from the engraving stylus 26 (in a manner and relationship to be explained below) is a magnetic pickup head 34. Situated farther along the circumference of the ring 32 is an erasing head 36 arranged continuously to wipe off any recording made upon the ring 32 so that the recording head 32 may again record upon a clean portion of the magnetic ring 32. The output of the pickup head 34 is fed into a power amplifier 38, the output of which actuates a makeready tool driver or actuator 40 which drives a makeready tool 42 forward and backward. As will be explained in more detail below, the makeready tool 42 may be in the nature of a grinder rotated by a high speed motor 44, the tool end being reciprocated by the makeready tool driver 40. However, the tool 42 may be a hot stylus of particularshape, as described below, where the plate material can be operated on by such a stylus; 1

Referring now to Fig. 2, showing schematically an exemplary mechanical arrangement, it is seen that the light source 10 and the photocell 14 are containedin a;

housing 46 mounted upon a carrier 48 which is arranged for reciprocation upon guide rods 50 and 52. For support of the image sheet to be scanned there is provided a cylinder 54 around which is wrapped the original copy or image sheet to be scanned by the photocell 14 while being illuminated by the'light source 10. A second carriage 56 also mounted for reciprocation along the guide rods 50 and 52 supports a housing 58 containing the engraving stylus 26 and the stylus motor 28. Adjustment of the stylus 26 for proper penetration depth is accomplished by means of a stylus control knob 60. Also' supported upon the carriage56 is a housing or carriage V 61 containing or supporting the makeready tool 42"and its actuator 49 to impart a reciprocating motion to the' makeready tool 42. As will be explained in more detail, there is also illustrated the motor 44 for imparting'a rotary motion to the makeready tool 42 when such action is required.

All the carriages move at identical rates, for instance by means connecting them together such as the inextensible tapes of the Boyajean patent,'and housings 58 and 61 may be on a single carriage, with the makeready tool disposed to operate on the same line of dots as the engraving "thereof. As already described, the engraving (in and out) motions of' stylus 26 are controlled by the scan signals amplified as illustrated in Fig. 1.

stylus, or in the space between adjacent lines For supporting the plate to be engraved there is provided a cylinder 62 around which the plate to be engraved is wrapped. The engraving plate cylinder 62 as well as the image sheet support cylinder 54 are rotated in synchronism by a power source not shown. The two cylinders 54 and 62 are mounted upon a common shaft comprised of two separate sections 64 and 66 coupled by a disengageable coupling 68. The coupling 68 includes a notched disc 70 and a complementary disc 72 provided with a pin 74 adapted accurately to engage the notch of disc 70 when these discs are moved axially (by means not shown) to effect engagement of the coupling.

Most conveniently, the time delay device may be provided as follows. Situated around the entire circumference of the plate cylinder 62 at the end adjacent the coupling plate 70, is the magnetic recording ring 32. The ring 32 may be in the form of a metallic tape, or a non-metallic base having magnetic particles coated thereon, or a separate metallic disc mounted upon the end of the plate cylinder 62. In Fig. 2, as in Fig. 1, the reference numeral 30 indicates the recording head which impresses upon the recording ring 32 the signals obtained fed from the tone control 20. Displaced along the circumference of the recording ring 32 is the magnetic pickup head 34, the output of which is amplified in the power amplifier 38 (Fig. 1), to power the makeready stylus vibrator or actuator 40. Spaced farther along the circumference of the magnetic recording ring 32 is the erasing head 36 which wipes off all signals recorded on the ring 32 and presents a fresh portion for recording to the recording head 30. It is obvious, referring to Fig. 1, that the delay device could equally well be elsewhere, both in the electrical and structural senses, so long as it is in the channel supplying signal power to the makeready tool.

To enable the makeready tool 42 to operate upon that portion of the engraving plate within which it is desired to reduce the height of the highlight dots, the makeready tool 42 must be displaced circumferentially from the engraving stylus 26 by an angular amount equal to the angular displacement between the recording head 30 and the pickup head 34. An alternative to this arrangement could be accomplished by the introduction of a suitable electrical delay in the circuit between the photocell amplifier 16 and the makeready stylus motor 40.

The makeready tool 42 may be of various types, as shown in Figs. 3A, 3B and 3C. For example, the makeready tool may be a heated stylus having a point angle larger than that of the stylus 26, and reciprocated toward and from the engraving sheet in response to the highlight dot signal picked up from the recording pickup head 34, amplified in the power amplifier 38 and then fed to the makeready actuator 40. An example of this type of makeready tool is shown in Fig. 3A, the obtuse angle being indicated at 40a. The dash lines in this figure indicate the relatively smaller included angle of the normal engraving stylus 26.

Another form of suitable makeready tool is illustrated in Fig. 3B and is designated as 40b. In this modification the tool is a hollow cone grinding wheel dimensioned such that when it is centered over a highlight dot and moved forward by the makeready tool actuator 40, the tops of the highlight dots will be ground off the desired amount.

Another modification of the makeready tool is indicated as 40c in Fig. 3C. In this form the makeready tool is a cone-shaped grinding wheel with an included angle greater than that of the engraving stylus 26. Thus as the makeready tool is advanced or thrust into the engraving plate, between adjacent highlight dots, the tops of the highlight dots will be lowered below the normal printing height. Fig. 4 illustrates this action diagrammatically.

While the tools so far described have been treated as rotating grinders, it is clear that, within the limitatipns of the material constituting the engraved plate, other deforming tools may be employed. Thus, for plastic plates, a heated tool might be used to deform the highlight dots, and for some materials, an embossing or other deforming operation could be employed.

It is understood that the positioning or orientation of the makeready tool is dependent upon which form or modification of makeready tool is to be utilized. For example, if the makeready tool to be utilized is of the form shown in Fig. 3B, one which acts upon the highlight dot top itself, such positioning will be slightly different from that required when the makeready tool is in the form such as illustrated in Fig. 3C or the heated obtuse stylus type of Fig. 3A, where the deforming action take place primarily between the highlight dots and secondarily on the highlight dots themselves.

Since the signals corresponding to highlight areas of the original may be either relatively small or relatively large (as compared with signals corresponding to shadow areas), depending upon whether the original is a positive or a negative, the term extreme intensity or amplitude is used in the subjoined claims to signify generally a signal region corresponding to highlight areas and to make it clear that the makeready tool is not operated in areas corresponding to shadows or intermediate tones, regardless of whether the final signal employed to control the makeready tool is relatively small or relatively large, so long as it does not include the middle region.

While there has been described in detail What is at present considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the following claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A machine for producing on a plate from an image sheet a screened relief pattern having halftone dots thereon suitable for image reproduction by printing processes and including a pair of synchronously movable members for individually supporting a plate and an image sheet, and a pair of reciprocable carriages individually including an image scanning system and a plate engraving tool respectively, means controlled by said image scanning system for operating said engraving tool to produce a pattern of halftone dots in accordance with the tone values of the image sheet including shadow dots and highlight dots, and means independent of the foregoing means and independently controlled by said image scanning system for selectively lowering the height of only said highlight dots produced by said plate engraving tool.

2. The invention as set forth in claim 1 in which said means for lowering the height of the highlight dots includes a tool for removing some of the material forming said dots.

3. The invention as set forth in claim 1 in which said last mentioned means includes a plate-material removing tool, and means for reciprocating said tool to bring it into contact with selected parts of said plate.

4. The invention as set forth in claim 1 in which said last mentioned means includes a plate-material removing tool, and means for reciprocating and rotating said tool.

5. A machine for producing on a plate from an image sheet a screened relief pattern having highlight dots thereon which is suitable for image reproduction by printing processes, comprising means for scanning an image, means controlled by said scanning means to engrave a plate to produce a screened relief pattern including highlight dots, and means including a delay mechanism and controlled by said scanning means to selectively modify the height of said highlight dots after such dots are formed.

6. In a machine for producing on a plate from an image sheet a screened relief pattern having highlight dots thereon and suitable for image reproduction by printing processes, the combination comprising a pair of synchronously movable members for individually supporting a plate and an image sheet, and a pair of reciprocating carriages individually including an image scanning system and a plate engraving tool respectively, a makeready tool mounted on the same carriage as said engraving tool, signal recording means controlled by said image scanning system, and actuating means controlled by said recording means to actuate said makeready tool.

7. The invention as set forth in claim 6, including means controlling said makeready tool so as to be actuated only by relatively extreme intensity signals from said scanning means.

8. In a machine for producing on a plate from an image sheet a screened relief pattern having highlight dots thereon and suitable for image reproduction by printing processes, the combination comprising a pair of synchronously movable members for individually supporting a plate and an image sheet, a pair of reciprocating carriages, one of said carriages carrying an image scanning system, the other of said carriages carrying an engraving tool and a makeready tool; a recording medium mounted on one of said movable members, a recording means controlled by said scanning system for producing a recording on said assnaae recording medium, a recording pickup mounted adjacent said recording medium, a makeready tool actuator, and

means for amplifying the output from said recording pickup to energize said makeready tool actuator.

9. The invention as set forth in claim 8 in which said recording medium comprises an endless band of material capable of magnetic recording.

10. The invention as set forth in claim 8 in Which said recording means is actuated only by relatively extreme intensity signals from said scanning means, which signals represent highlights on said image sheet.

References Cited in the file of this patent UNITED STATES PATENTS 

